Flame-spread rating: any surface that would be exposed by cutting through…

[sunyaer]

The following is from Ontario Building Code, division B, part 3
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3.1.5.10. Combustible interior Finish
…
(2) Combustible interior wall finishes, other than foamed plastics, are permitted in a buildingrequired to be of noncombustible constructionprovided they,

(a) are not more than 25 mm thick, and

(b) have a flame-spread rating not more than 150 on any exposed surface, or any surface that would be exposed by cutting through the material in any direction.
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Is there a real example where “any surface that would be exposed by cutting through the material in any direction” would need to be examined for having a flame-spread rating not more than 150 ?

 

[tmurray]

This is worded this way to deal with factory assembled building components and field constructed. A good example would be freezer wall and ceiling panels. These have a foam insulation core with a metal covering all around. If we just looked at the outside of the material, we would just be evaluating the metal. But due to the wording, we need to evaluate the foam core as well.

 

[sunyaer]

This is worded this way to deal with factory assembled building components and field constructed. A good example would be freezer wall and ceiling panels. These have a foam insulation core with a metal covering all around. If we just looked at the outside of the material, we would just be evaluating the metal. But due to the wording, we need to evaluate the foam core as well.

Would the foam core be exposed for any reason?

 

[tmurray]

Not usually. The only time you would is if there was some form of field modification, or if the panel gets damages over time.

 

[sunyaer]

I would like to add some thoughts here contributed from a forum member in private conversation who is no longer replying in posts:

if you have a 4 foot by 8 foot wood panel

When installing it you have to cut it to size

You expose a surface,,,, that surface has to have a flame-spread rating not more than 150 on any exposed surface.

So basically, the wording any surface that would be exposed by cutting through the material in any direction is to ensure that any possibly exposed surface during construction has to have the required flame-spread rating. In most cases, this could also be understood as the material being homogeneous throughout, see screenshot and attached file.

 

[Inspector Gadget]

It also applies to things like Zipsystem sheathing - OSB over foam.

Better example might be foil-backed polyisocyanurate insulation panels.